The respiratory mask typically worn by aircraft crewmembers must be attached surely and rapidly on the crewmember head. And it must be attached on an one-handed basis, since the user's other hand is frequently occupied in some other essential task.
For example, if because of a pressurization failure, the pilot of an aircraft is required rapidly to don his respiratory mask to provide the necessary oxygen for breathing, he often must do so with one hand while his other hand is occupied in controlling the aircraft. Thus, the use of an inflatable head harness has been suggested in order to permit the respiratory mask to be donned using only one hand. The head harness is expanded diametrically by the introduction of pressurized gas to cause the harness to increase in size so that it can be positioned over the head of the user. The gas flow is controlled by a valve attached to the respiratory mask, and, after enlargement, the respiratory mask is placed in position over the nose and mouth, with the head harness extended over and spaced from the back of the head. Once the respiratory mask has been properly positioned, the pressure in the head harness is released, causing the harness to contract and to contact the head of the pilot, whereby the respiratory mask is securely held in its proper position. Meanwhile, the pilot's other hand is free to control the aircraft or to perform such other tasks as may be required.
An inflatable head harness is shown and described in U.S. Pat. No. 3,599,636 in which the harness is defined by a pair of spaced, expandable rubber tubes which are housed within an outer casing of material which has limited yieldability and which is initially in pleated form.
The disclosed harness needs to work a minimum pressure of 6 bars at the arrival of breathing gas.
However, more and more often, the breathing gas supply system of aircraft uses Onboard Oxygen Generating System, or OBOGS, which delivers breathing gas at a maximum pressure of 4 to 5 bars. This pressure is not sufficient to inflate correctly the usual inflatable harness for allowing the crewmember to install the mask easily.
Therefore, there is a need for an apparatus which allows the use of inflatable harness with the pressure level delivered by OBOGS.